How to unhide hidden objects with a Python script?
As of Blender 2.81, Object.hide_set() is working properly and seems to be the equivalent of Object.hide property in 2.7x versions.

Proof using the console:

&gt;&gt;&gt; bpy.context.object.hide_set(False)


To unhide multiple objects you can run over objects in the scene and call the setter per object:

for o in ("Cube", "Camera", "Light"):
   obj = bpy.context.scene.objects.get(o)
   #if obj: obj.hide_viewport = False
   if obj: obj.hide_set(False)


You can also iterate through any given collection:

col = bpy.data.collections.get("Collection")
if col:
   for obj in col.objects:
       obj.hide_set(False)


Whatever you like...